Surface improvement of additively manufactured articles produced with aluminum alloys

ABSTRACT

A method for improving the surface of an aluminum alloy article includes manufacturing the aluminum alloy article using an additive manufacturing technique, wherein the article as-manufactured includes one or more of cracks, roughness, or porosity at a surface of the article; coating the surface of the aluminum alloy article with a diffusion element, the diffusion element being capable of diffusing at least 0.2 mils into the article; heating the aluminum alloy article coated with the diffusion element to cause the diffusion element to diffuse the at least 0.2 mils into the article, thereby forming a diffusion layer of at least 0.2 mils in thickness comprising both aluminum alloy and diffusion element; and removing the diffusion layer from the aluminum alloy article, whereby upon the removing, a resulting improved surface of the article comprises fewer or smaller cracks, reduced roughness, or reduced porosity.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/933,154, filed on Nov. 5, 2015, the contents of which are hereinincorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure generally relates to additive manufacturingtechnologies. More particularly, the present disclosure relates tosurface improvement of additively manufactured articles produced withaluminum alloys.

BACKGROUND

Additive manufacturing (AM) processes, such as Direct Laser Metal Fusion(DMLF), have recently come to prominence as a cost-effective alternativeto traditional manufacturing techniques. However, external and internal(e.g., hollow or cored) surfaces of articles formed by AM can exhibitsurface roughness associated with the application of successive layersor the unintended clinging of powder particles to the free edges, asshown in FIG. 1. Internal defects and surface connected defects, likethose shown in FIG. 2, may render a component unusable.

Prevention of this roughness condition may not be critical if thesurface can be subsequently improved in a cost-effective manner To theextent that such mechanical surface roughness is non-conforming with theengineering design intent or for cosmetic reasons, a means of smoothingthe surface (or controlled excess stock removal) is desired, especiallythose surfaces which are inaccessible to hand-finishing ormachine-finishing methods. Additionally, justification for requiredsurface improvement, encapsulation, and subsequent hot isostatic press(HIP) processing extends to various metallurgical reasons including 1)smoothing undesirable surface roughness, 2) smoothing roughness toenable subsequent encapsulation of surface connected porosity anddefects for HIP processing to eliminate internal and surface defects inthe AM component, 3) removal of metallurgical surface defects such asmicro cracking, and 4) being able to predicatively remove excess stockor non-conforming layers without creating metallurgical issues.

U.S. Pat. No. 8,506,836 discloses surface finish and encapsulationtechnologies for nickel-based alloys, but to date no such technology hasever been developed for aluminum alloys. For aluminum alloys, mechanicalor electro-polish smoothing of external surfaces may reduce roughness,as shown in FIG. 3, but they may not enable surface connected defects tobe eliminated in HIP processing. Thus, encapsulation is required tobridge the surface defects to enable successful HIP processing. U.S.Pat. Nos. 2,654,701 and 3,993,238 disclose zincate plating for aluminum,but they do not disclose diffusing the zinc into the substrate followedby subsequent stripping to enhance surface finish and enable successfulencapsulation.

Accordingly, there remains a need in the art for surface improvement ofadditively manufactured articles produced with aluminum alloys.Furthermore, other desirable features and characteristics of thedisclosure will become apparent from the subsequent detailed descriptionand the appended claims, taken in conjunction with the accompanyingdrawings and this background of the disclosure.

BRIEF SUMMARY

The present disclosure relates to surface improvement of additivelymanufactured articles produced with aluminum alloys. In one exemplaryembodiment, a method for improving the surface of an aluminum alloyarticle includes manufacturing the aluminum alloy article using anadditive manufacturing technique, wherein the article as-manufacturedincludes one or more of cracks, roughness, or porosity at a surface ofthe article; coating the surface of the aluminum alloy article with adiffusion element, the diffusion element being capable of diffusing atleast 0.2 mils into the article; heating the aluminum alloy articlecoated with the diffusion element to cause the diffusion element todiffuse the at least 0.2 mils into the article, thereby forming adiffusion layer of at least 0.2 mils in thickness comprising bothaluminum alloy and diffusion element; and removing the diffusion layerfrom the aluminum alloy article, whereby upon the removing, a resultingimproved surface of the article comprises fewer or smaller cracks,reduced roughness, or reduced porosity.

This summary is provided to describe select concepts in a simplifiedform that are further described in the Detailed Description. Thissummary is not intended to identify key or essential features of theclaimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and wherein:

FIG. 1 is an image of an article of manufacture made with additivemanufacturing techniques, which exhibits surface roughness that wouldrender it unsuitable for subsequent HIP processing;

FIG. 2 is an image of an article of manufacture made with additivemanufacturing techniques, which exhibits surface connected defects andinternal defects that can be improved via encapsulation and HIPprocessing;

FIG. 3 is an image of an article of manufacture made with additivemanufacturing techniques, which exhibits an external surface that hasbeen smoothed via electro-chemical means, yet which still exhibits aninternal surface having roughness that would render it unsuitable forsubsequent HIP processing;

FIG. 4 is a flow diagram illustrating steps in a method for surfaceimprovement of additively manufactured articles produced with aluminumalloys in accordance with an exemplary embodiment of the presentdisclosure;

FIG. 5 is a flowchart illustrating a method for manufacturing thearticle using additive manufacturing techniques in accordance with anexemplary embodiment;

FIG. 6, which is a schematic view of an AM system for manufacturing thearticle in accordance with an exemplary embodiment; and

FIG. 7 illustrates an article of manufacture having its surfacessmoothed using techniques in accordance with embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. As used herein, the word “exemplary” means “serving as anexample, instance, or illustration.” Thus, any embodiment describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. All of the embodiments describedherein are exemplary embodiments provided to enable persons skilled inthe art to make or use the invention and not to limit the scope of theinvention which is defined by the claims. Furthermore, there is nointention to be bound by any expressed or implied theory presented inthe preceding technical field, background, brief summary, or thefollowing detailed description.

As used herein, the term “aluminum alloy” refers to any alloy whereinaluminum is the single greatest constituent thereof, as measured on aweight percentage basis. One example of this is the class of alloyswhere aluminum consists of a majority of the alloy, as measured on aweight percentage basis. To give some non-limiting examples of aluminumalloys, the following cast and wrought alloys may be utilized. Castalloys like 201 from the difficult to cast 200 series, or 355, 356, or357 from the 300 series may be employed. Wrought alloys like 6061 fromthe weldable 6000 series or 7075 from the high-strength 7000 series maybe utilized. Other alloys may also be employed as are well-known tothose having ordinary skill in the art, such as the utilization ofaluminum alloy 8009 in additive manufacturing applications. Conventionalcast or wrought aluminum alloys may be modified and optimized foradditive manufacturing. The rapid solidification rates at which thesealloys are deposited, layer by layer, allow for the creation of uniquemicrostructures using various additive elements that could not berealized using ordinary cast/wrought alloy techniques. For purposes ofthis disclosure, this newer class of aluminum alloys will be referred toas “non-conventional” aluminum alloys. An exemplary, a class ofnon-conventional alloys includes those known as “rapidly solidifiedpowder aluminum alloys”, such as 7090 and 7091.

FIG. 4 is a flow diagram illustrating steps in a method 100 for surfaceimprovement of additively manufactured articles produced with aluminumalloys in accordance with an exemplary embodiment of the presentdisclosure. The method 100 includes a first step 110 of forming, usingan additive manufacturing process, an article of manufacture having atleast one surface. In some examples, the article of manufacture has bothinterior and exterior surfaces. Additive manufacturing processes can beused to produce complex geometries in a single operation with notooling. Additive manufacturing technology allows for the article to beproduced at a net-shape or near-net shape without the application of theheating, casting, or forging processes commonly used in the prior art.Thus, as used herein, the term additive manufacturing refers to anyprocess wherein thin successive layers of material are laid down atopone another to form an article.

FIG. 5 is a flowchart illustrating a method 200 for manufacturing thearticle using additive manufacturing techniques. In a first step 210, amodel, such as a design model, of the article may be defined in anysuitable manner For example, the model may be designed with computeraided design (CAD) software and may include three-dimensional (“3D”)numeric coordinates of the entire configuration of the componentincluding both external and internal surfaces. In one exemplaryembodiment, the model may include a number of successive two-dimensional(“2D”) cross-sectional slices that together form the 3D component.

In step 220 of the method 200, the article is formed according to themodel of step 210. In one exemplary embodiment, the entire component isformed using a rapid prototyping or additive layer manufacturingprocess. Some examples of additive layer manufacturing processesinclude: selective laser sintering in which a laser is used to sinter apowder media in precisely controlled locations; laser wire deposition inwhich a wire feedstock is melted by a laser and then deposited andsolidified in precise locations to build the product; electron beammelting; laser engineered net shaping; and direct metal deposition. Ingeneral, additive manufacturing techniques provide flexibility infree-form fabrication without geometric constraints, fast materialprocessing time, and innovative joining techniques. In one particularexemplary embodiment, direct metal laser fusion (DMLF) is used toproduce the article in step 220. DMLF is a commercially-available,laser-based rapid prototyping and tooling process by which complex partsmay be directly produced by precision melting and solidification ofmetal powder into successive layers of larger structures, each layercorresponding to a cross-sectional layer of the 3D component.

As such, in one exemplary embodiment, step 220 is performed with DMLFtechniques to form the article. However, prior to a discussion of thesubsequent method steps, reference is made to FIG. 6, which is aschematic view of a DMLF system 300 for manufacturing the article inaccordance with an exemplary embodiment.

Referring to FIG. 6, the system 300 includes a fabrication device 310, apowder delivery device 330, a scanner 340, and a laser 360 that functionto manufacture the article 350 (e.g., the article) with build material370. The fabrication device 310 includes a build container 312 with afabrication support 314 on which the article 350 is formed andsupported. The fabrication support 314 is movable within the buildcontainer 312 in a vertical direction and is adjusted in such a way todefine a working plane 316. The delivery device 330 includes a powderchamber 332 with a delivery support 334 that supports the build material370 and is also movable in the vertical direction. The delivery device330 further includes a roller or wiper 336 that transfers build material370 from the delivery device 330 to the fabrication device 310.

During operation, a base block 340 may be installed on the fabricationsupport 314. The fabrication support 314 is lowered and the deliverysupport 334 is raised. The roller or wiper 336 scrapes or otherwisepushes a portion of the build material 370 from the delivery device 330to form the working plane 316 in the fabrication device 310. The laser360 emits a laser beam 362, which is directed by the scanner 340 ontothe build material 370 in the working plane 316 to selectively fuse thebuild material 370 into a cross-sectional layer of the article 350according to the design. More specifically, the speed, position, andother operating parameters of the laser beam 362 are controlled toselectively fuse the powder of the build material 370 into largerstructures by rapidly melting the powder particles that may melt ordiffuse into the solid structure below, and subsequently, cool andre-solidify. As such, based on the control of the laser beam 362, eachlayer of build material 370 may include unfused and fused build material370 that respectively corresponds to the cross-sectional passages andwalls that form the article 350. In general, the laser beam 362 isrelatively low power to selectively fuse the individual layer of buildmaterial 370. As an example, the laser beam 362 may have a power ofapproximately 50 to 500 Watts, although any suitable power may beprovided.

Upon completion of a respective layer, the fabrication support 314 islowered and the delivery support 334 is raised. Typically, thefabrication support 314, and thus the article 350, does not move in ahorizontal plane during this step. The roller or wiper 336 again pushesa portion of the build material 370 from the delivery device 330 to forman additional layer of build material 370 on the working plane 316 ofthe fabrication device 310. The laser beam 362 is movably supportedrelative to the article 350 and is again controlled to selectively formanother cross-sectional layer. As such, the article 350 is positioned ina bed of build material 370 as the successive layers are formed suchthat the unfused and fused material supports subsequent layers. Thisprocess is continued according to the modeled design as successivecross-sectional layers are formed into the completed desired portion,e.g., the component of step 220.

The delivery of build material 370 and movement of the article 350 inthe vertical direction are relatively constant and only the movement ofthe laser beam 362 is selectively controlled to provide a simpler andmore precise implementation. The localized fusing of the build material370 enables more precise placement of fused material to reduce oreliminate the occurrence of over-deposition of material and excessiveenergy or heat, which may otherwise result in cracking or distortion.The unused and unfused build material 370 may be reused, thereby furtherreducing scrap.

Any suitable laser and laser parameters may be used, includingconsiderations with respect to power, laser beam spot size, and scanningvelocity. The build material 370 is provided as an aluminum alloy inpowder form. As we noted initially above, non-limiting examples of suchaluminum alloys include 201, 355, 356, 357, 6061, and 7075. In general,the powder build material 370 may be selected based on one or more ofstrength, durability, and useful life, particularly at hightemperatures, although it should be appreciated that the powder buildmaterial 370 may also be selected based on the intended function of thearticle being formed. The powdered form of the alloy is produced bycombining the various constituents (metals and other elements) of thealloy into a mixture, melting the mixture, and atomizing the meltedmixture to form a powder, a process which is well-known in the art.

Returning to FIG. 5, at the completion of step 220, the article may begiven a stress relief treatment, and then is removed from the additivemanufacturing system (e.g., from the DMLF system 300). In optional step230, the component formed in step 220 may undergo finishing treatments.Finishing treatments may include, for example, polishing, peening,and/or the application of coatings. If necessary, the component may bemachined to final specifications. The article, produced using additivemanufacturing techniques, has a layer-by-layer fused microstructure thatexhibits anisotropic mechanical and physical properties. It should benoted that these “finishing treatments” of optional step 230, ifpresent, are performed separately from and in addition to the plating,diffusing, stripping, and HIP procedures as are described in greaterdetail below in connection with the surface improvement processes of thepresent disclosure.

Returning to FIG. 4, after the article 350 has been formed with thealuminum alloy using the additive manufacturing process as describedabove with regard to step 110 of method 100, it should be expected thatthe article 350 will exhibit surface roughness, as illustrated in detailin FIGS. 1-3. This roughness would prevent the use and/or successfulapplication of beneficial HIP processing techniques to improve thearticle 350. Thus, in accordance with embodiments of the presentdisclosure method 100 continues with the diffusion of an element (orelements) into the surface of the AM aluminum article, followed byselectively removing the diffusion layer without detrimental attack ofthe aluminum substrate. In the course of doing so, the rough surface ofarticle 350 is rendered smoother as has been demonstrated in FIG. 7,which is prophetic. This described operation can be performed repeatedlyat appropriate steps in the overall manufacturing sequence, and thediffusion cycle can be sequenced with the component heat treatmentcycle.

Thus, FIG. 4 illustrates a step 120, performed after step 110, where adiffusion element is coated onto the aluminum alloy article ofmanufacture, namely onto its surfaces, including both internal andexternal surfaces if present. One particular embodiment uses zinc as thediffusion element and plating as the coating process, and starts with aconventional zincate plating process for aluminum alloys, widely used asstarting point or bond coat for various other plating processes. In theprior art, such coatings are done after all heat treating is completed.For example, the zincate plating process refers to the alkalinesolutions used in a dipping (immersion) process to plate aluminum withzinc. This immersion process is electroless (i.e., not electroplating)and involves the displacement of zinc from zincate by aluminum:

→3 Zn(OH)₄ ²⁻+2 Al→3 Zn+2 Al(OH)₄ ⁻+4 OH⁻

Alternatively, tin, silver, gold, copper, nickel or other elements maybe electroless coated or electro-plated onto the aluminum alloy insteadof zinc; a combination of several different elements or platings may beadvantageous depending on the specific application and embodiment. Thecoating material is ideally metallic and capable of subsequent diffusioninto the article 350 to form a diffusion coating. Moreover, plating orelectroless plating should not be considered the only suitable coatingtechnique. Rather, other coating processes such as spray-basedprocesses, deposition-based processes, non-aqueous plating, molten saltbaths, pack plating, and others may be used as well. The diffusionelement may be applied to an internal surface of the article 350 toensure that the coating material layer spans the surface-connectedporosity and any cracks within. Some coatings may be more advantageousfor their ability to encapsulate by forming a more continuous layerbetter suited for subsequent HIP (to improve the internal structure),and not necessarily form a diffusion layer. A particular purpose ofdiffusion coating is to enable subsequent removal to enhance the surfacesmoothness and metallurgy. While possible that one coating will do both,that is not necessary with proper sequencing. In some situations, it maybe advantageous to perform diffusion coating and removal to improveexterior surfaces followed by encapsulation and HIP to improve bothinterior and exterior surfaces. Instead of removing an encapsulatingcoating of gold, nickel, etc., leaving such coatings in place may bebeneficial to corrosion resistance, etc.

Once the article 350 has been coated with the diffusion element, method100 continues with a step 130 of heat treating the article 350 and thecoating material layer to diffuse the diffusion element and to form thediffusion coating on the article 350. The diffusion coating comprises asurface additive layer and a diffusion zone or layer below the surfaceadditive layer. The surface additive layer is the coating material layerdepleted in one or more elements after diffusing into the parent metalof the material substrate.

Diffusion heat treating may be performed at elevated temperatures ofbetween about 350° C. to about 475° C. (662-887° F.) for about two hoursto about twenty hours. Slow ramping through the melting point of thecoating element or eutectics formed during diffusion may be desirable toovercome objectionable melting of this “sacrificial in-process layer”.In other embodiments, the diffusion heat treatment may occur at atemperature and/or for a time period (duration) outside of theaforementioned ranges. After diffusion heat treating, the article 350may be cooled.

During the coating step 120, if performed at a sufficiently elevatedtemperature, a primary diffusion zone occurs to some degree between thecoating material layer and the substrate as a result of theconcentration gradients of the constituents. At elevated temperatures ofthe diffusion heat treating step 130, further inter-diffusion occurs asa result of solid-state diffusion across a coating bond line. Thecoating bond line is the demarcation between the applied coatingmaterial layer and the substrate. The coating bond line is the “edge” ofthe article 350.

A thickness of the diffusion layer of about 0.2 to about 3 mils isoptimal, and corresponds to how much of the upper portion of thesubstrate of the first intermediate article will be removed insubsequently described steps. Diffusion time and temperature may becontrolled to achieve the desired thickness. If significant surfaceroughness and surface-connected defects exist, a thicker diffusioncoating may be necessary. Internal passage surface diffusion layers maybe thinner than diffusion layers on external surfaces and steps can betaken to selectively reduce the thickness of the diffusion layer on theexternal surfaces to arrive at a more even diffusion coating overall tobetter hold dimensions following removal of the diffusion coating, ashereinafter described. To reach internal or hollow portions of thearticle, the diffusion element (for example, zincate solution) may beflowed through the article. To reach “dead-end” passages, vacuumimpregnation may be employed.

Still referring to FIG. 4, according to exemplary embodiments, method100 continues with a step 140 of removing the diffusion coating (alsoreferred to herein as “stripping”) to improve the surface of the article350. The layers of the diffusion coating are substantially removed intheir entirety to the coating diffusion boundary thereby forming theimproved surface. As the diffusion layer includes the upper portion ofthe substrate, the upper portion of the substrate will also be removed.The diffusion coating and removal steps function to reduce surfaceroughness, resulting in the article 350 having enhanced surfaces. Thecoating diffusion boundary should be sufficiently defined or sharp suchthat removal of the diffusion coating yields a substrate surfacecomposition close to that of the original substrate.

The diffusion coating may be removed by any known diffusion coatingremoval technique, including mechanical, chemical, electro-chemical, orany suitable combination thereof. For example, the cooled component maybe flushed inside and out in a chemical solvent such as ferric chloride,nitric acid, etc. The chemical solvent is selected for its ability toremove the diffusion coating, without affecting the integrity of thealuminum alloy article 350. The coating removal chemical compositionsand concentrations may be modified to optimize the amount of diffusioncoating removed and/or the removal time while maintaining the integrityof the substrate. The dimensions of the original model for the componentmay be modified to accommodate removal of the upper portion of theoriginal substrate above the coating diffusion boundary to allow thefinished component to meet finished component dimensions. The strippingprocess can be dependent on the particular aluminum alloy, andelectrochemical stripping may be used. In another embodiment forstripping, the diffusion layer is removed by forming an anodic aluminumoxide (anodize) coating on the diffusion layer and then removing thecombined diffusion/anodize coating chemically.

If, after performing steps 120-140, there is residual surface roughnessor surfaces with inadequate diffusion bonded faying surfaces (“diffusionbonding failures”), forming of the diffusion coating (applying anddiffusion heat treating steps) and removal thereof (hereinaftercollectively a “forming and removing cycle”) may optionally be repeatedas many times as necessary until the at least one surface of the articleis sufficiently enhanced, the sufficiency thereof known to one skilledin the art. As noted above, the term “enhanced” or the like refers to areduction in surface roughness and/or improvement in metallurgicalquality. The improvement in metallurgical quality results from removingsurfaces lacking sufficient metallurgical surface integrity caused byinadequately metallurgically diffusion bonded faying surfaces of thesurface-connected cracks.

After the one or more forming and removing cycles are performed, themethod 100 may continue with an encapsulation step 150. An encapsulationlayer functions to effectively convert the surface porosity and cracksinto internal porosity and cracks. Any suitable encapsulation processmay be performed that bridges and covers the porosity and cracks in atleast one surface of the article. For example, the encapsulation layermay have a thickness of approximately 10-100 μm, although any suitablethickness may be provided. Such encapsulation layer may be subsequentlyremoved or maintained to function as an oxidation protection layer. Theencapsulation layer may be a metal or alloy that is compatible with thesubstrate material and may be formed, for example, by a plating processor a coating process. In various exemplary embodiments, theencapsulation layer may be formed for example, by electroless plating orelectroplating processes. In further embodiments, the encapsulationlayer may be formed by processes including cobalt plating, sol-gelchemical deposition techniques, or low pressure plasma sprays. Asuitable material for the encapsulation layer is one which when appliedor when heated to the HIP temperature is relatively ductile and free ofgaps or cracks and which spans the surface-connected porosity and crackswithin, for example, internal passages of the aluminum alloy article350.

After encapsulation, the method 100 may continue with a HIP processingstep 160. In the hot isostatic pressing (HIP) process, the article 350is subjected to elevated temperatures and pressures over time. HIPprocessing reduces or substantially eliminates internal void defects,such as porosity or cracks. The HIP process may be performed at anytemperature, pressure, and time that are suitable for diffusion bondingand forming a compacted solid having minor or acceptable levels ofporosity, but substantially free of cracks. For example, the HIP processmay be performed at a processing temperature in a range of about 480° C.to about 530° C. and may be performed at a pressure in a range of about1 ksi to about 25 ksi for a time period of about 1 to about 10 hours. Inother embodiments, the HIP processing temperature, pressure, and timemay be higher or lower to form a compacted article having negligiblecracks and porosity. The consolidated article 350 may comprise thefinished component.

Accordingly, the disclosed are methods for surface improvement ofadditively manufactured articles produced with aluminum alloys. Themethods diffuse an element into the surface of the aluminum alloyarticle, and then strip the diffusion layer to create an enhancedsurface.

In this document, relational terms such as first and second, and thelike may be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. Numericalordinals such as “first,” “second,” “third,” etc. simply denotedifferent singles of a plurality and do not imply any order or sequenceunless specifically defined by the claim language. The sequence of thetext in any of the claims does not imply that process steps must beperformed in a temporal or logical order according to such sequenceunless it is specifically defined by the language of the claim. Theprocess steps may be interchanged in any order without departing fromthe scope of the invention as long as such an interchange does notcontradict the claim language and is not logically nonsensical.

Furthermore, depending on the context, words such as “connect” or“coupled to” used in describing a relationship between differentelements do not imply that a direct physical connection must be madebetween these elements. For example, two elements may be connected toeach other physically, electronically, logically, or in any othermanner, through one or more additional elements.

While at least one exemplary embodiment has been presented in theforegoing detailed description of the invention, it should beappreciated that a vast number of variations exist. It should also beappreciated that the exemplary embodiment or exemplary embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the invention in any way. Rather, the foregoingdetailed description will provide those skilled in the art with aconvenient road map for implementing an exemplary embodiment of theinvention. It being understood that various changes may be made in thefunction and arrangement of elements described in an exemplaryembodiment without departing from the scope of the invention as setforth in the appended claims.

What is claimed is:
 1. A method for improving the surface of an aluminumalloy article comprising: manufacturing the aluminum alloy article usingan additive manufacturing technique, wherein the article as-manufacturedcomprises one or more of cracks, roughness, or porosity at a surface ofthe article; coating the surface of the aluminum alloy article with anencapsulating element, which may or may not also be a diffusion element,to facilitate HIP response; coating the surface of the aluminum alloyarticle with a diffusion element, the diffusion element being capable ofdiffusing at least 0.2 mils into the article, wherein the diffusionelement is selected from the group consisting of: electroless silver,gold, copper, and nickel; heating the aluminum alloy article coated withthe diffusion element to cause the diffusion element to diffuse the atleast 0.2 mils into the article, thereby forming a diffusion layer of atleast 0.2 mils in thickness comprising both aluminum alloy and diffusionelement; and removing the diffusion layer from the aluminum alloyarticle, whereby upon the removing, a resulting improved surface of thearticle comprises fewer or smaller cracks, reduced roughness, or reducedporosity.
 2. The method of claim 1, wherein the aluminum alloy articlecomprises an aluminum alloy selected from the group consisting of: castalloys and wrought alloys.
 3. The method of claim 1, wherein theadditive manufacturing technique is selected from the group consistingof: direct metal laser sintering, direct metal laser fusion, electronbeam melting, and selective laser sintering.
 4. The method of claim 1,wherein coating the surface comprises an electroless plating process orwherein coating the surface comprises an electrolytic plating process.5. The method of claim 1, wherein the diffusion element diffuses atleast 1 mil into the article.
 6. The method of claim 1, furthercomprising repeating the steps of coating, heating, and removing anadditional one or more times.
 7. The method of claim 6, wherein coatingwith the encapsulating occurs after the removing step.
 8. The method ofclaim 1, further comprising hot isostatic pressing the article.
 9. Themethod of claim 1, wherein hot isostatic pressing occurs after theremoving step.
 10. The method of claim 1, wherein the aluminum alloyarticle is a component of a gas turbine engine.
 11. A method forreducing roughness, porosity, and cracking of the surface of an aluminumalloy article comprising: manufacturing the aluminum alloy article usingan additive manufacturing technique, wherein the article as-manufacturedcomprises one or more of cracks, roughness, or porosity at a surface ofthe article; coating the surface of the aluminum alloy article with anencapsulating element, which may or may not also be a diffusion element,to facilitate HIP response; coating the surface of the aluminum alloyarticle with a diffusion element, wherein the diffusion element isselected from the group consisting of: electroless silver, gold, copper,and nickel, the diffusion element being capable of diffusing at least0.2 mils (5 microns) into the article; heating the aluminum alloyarticle coated with the diffusion element at a temperature between 350°C. to 475° C. for a time period of 2 to 20 hours to cause the diffusionelement to diffuse the at least 0.2 mils (5 microns) into the article,thereby forming a diffusion layer of at least 0.2 mils (5 microns) inthickness comprising both aluminum alloy and diffusion element; andremoving the diffusion layer from the aluminum alloy article using achemical solvent of ferric chloride or nitric acid, whereby upon theremoving, a resulting improved surface of the article comprises fewer orsmaller cracks, reduced roughness, or reduced porosity, wherein coatingwith the encapsulating element occurs after the removing step.
 12. Themethod of claim 11, wherein the aluminum alloy composition comprises amajority aluminum on a weight basis, and wherein the aluminum alloyarticle comprises an aluminum alloy selected from the group consistingof: cast alloys, wrought alloys, derivatives of said cast or wroughtalloys.
 13. The method of claim 11, wherein the additive manufacturingtechnique is selected from the group consisting of: direct metal lasersintering, direct metal laser fusion, electron beam melting, andselective laser sintering.
 14. The method of claim 11, wherein thediffusion element diffuses at least 1 mil (25 microns) into the article.15. The method of claim 11, further comprising repeating the steps ofcoating, heating, and removing an additional one or more times.
 16. Themethod of claim 11, further comprising hot isostatic pressing thearticle.
 17. The method of claim 11, wherein hot isostatic pressingoccurs after the removing step.
 18. The method of claim 11, wherein thealuminum alloy article is a component of a gas turbine engine.
 19. Amethod for reducing roughness, porosity, and cracking of the surface ofan aluminum alloy article comprising: manufacturing the aluminum alloyarticle using an additive manufacturing technique, wherein the articleas-manufactured comprises one or more of cracks, roughness, or porosityat a surface of the article; coating the surface of the aluminum alloyarticle with an encapsulating element, which may or may not also be adiffusion element, to facilitate HIP response; coating the surface ofthe aluminum alloy article with a diffusion element, wherein thediffusion element is selected from the group consisting of: electrolesssilver, gold, copper, and nickel; heating the aluminum alloy articlecoated with the diffusion element to cause the diffusion element todiffuse into the article, thereby forming a diffusion layer comprisingboth aluminum alloy and diffusion element; and removing the diffusionlayer from the aluminum alloy article using a chemical solvent of ferricchloride or nitric acid, whereby upon the removing, a resulting improvedsurface of the article comprises fewer or smaller cracks, reducedroughness, or reduced porosity, wherein coating with the encapsulatingelement occurs after the removing step.
 20. The method of claim 19,wherein the aluminum alloy article is a component of a gas turbineengine.